AJP - Cell Physiology, Vol 256, Issue 6 C1153-C1159, Copyright © 1989 by American Physiological Society
GABA-induced chloride current in rat isolated Purkinje cells
M. Kaneda, M. Wakamori and N. Akaike
Department of Physiology, Faculty of Medicine, Kyushu University, Japan.
Electrical and pharmacological properties of the gamma-aminobutyric acid
(GABA)-induced current in the rat isolated cerebellar Purkinje cell bodies
were studied using a concentration-jump method, which is termed as a
"concentration-clamp" technique. This technique enables the rapid exchange
of external solution around the neurons to be perfused internally under a
voltage-clamp condition. The peak amplitude of GABA response increased
sigmoidally with the increase of the concentration of GABA. The value of
the GABA concentration that evokes a half-maximal response (Ka) was 5 X
10(-5) M, and the Hill coefficient was 1.8. The current-voltage
relationship for the GABA response showed nonlinearity at membrane
potentials more negative than -40 mV. The reversal potential of GABA-evoked
current was close to the equilibrium potential of Cl- (ECl), indicating
that the current elicited by GABA is carried by Cl-. Both the activation
and inactivation phases of GABA-induced Cl- current (ICl) consisted of fast
and slow components. These time constants in both phases decreased as the
concentration of GABA increased. Strychnine and bicuculline inhibited the
GABA-induced ICl in a dose-dependent manner, and the inhibition of the GABA
response by bicuculline was competitive. Pentobarbital sodium augmented the
GABA response and modified the inactivation phase. The augmentation of the
GABA response by pentobarbital was more profound at lower concentrations of
GABA and was accompanied by a change in the Hill coefficient from 2 to 1.
The properties of the GABA response in cerebellar Purkinje cells were
thought to be basically similar to those previously reported in other
preparations.
